Decoration of NiFe-LDH Nanodots Endows Lower Fe-d Band Center of Fe-1-N-C Hollow Nanorods as Bifunctional Oxygen Electrocatalysts with Small Overpotential Gap

Single-atom Fe-N-C (denoted as Fe-1-N-C) catalysts exhibit inadequate bifunctional activities to conquer the sluggish oxygen reduction and evolution reaction (ORR/OER), hindering their practical applications in rechargeable Zn-air batteries (ZABs). Here, by employing Fe-1-N-C hollow nanorods as ORR-active support, OER-active NiFe-layered double hydroxide (NiFe-LDH) nanodots are evenly decorated through a spatially confined process to form NiFe-LDH/Fe-1-N-C heterostructure hollow nanorods with abundant accessible catalytic sites. The NiFe-LDH/Fe-1-N-C heterostructure not only enhances the ORR activity of pristine Fe-1-N-C but also realizes efficient bifunctional ORR/OER activity in one monolithic catalyst. Theoretical calculations reveal that introducing NiFe-LDH nanodots results in donation of electrons to the Fe-1-N-C matrix and thus lowers the Fe-d band center of the Fe-N-4 sites, dramatically narrowing the energy barriers of the ORR rate-limiting steps. As a result, NiFe-LDH/Fe-1-N-C nanorods deliver remarkable ORR activity with a half-wave potential of 0.90 V versus reversible hydrogen electrode, surpassing bare Fe-1-N-C and commercial Pt/C. Impressively, the integrated NiFe-LDH/Fe-1-N-C catalysts show outstanding bifunctional performance with a small overpotential gap of only 0.65 V. The liquid-state ZABs with NiFe-LDH/Fe-1-N-C as an air-cathode catalyst deliver a peak power density of 205 mW cm(-2) and long-term cycling stability of up to 400 h.